Scoring breakdown

With summer just around the corner, car buyers' thoughts are turning to convertibles. The change of seasons is a traditional trigger for fashion-conscious, well-heeled motorists to take stock of the drop-tops that have arrived during the colder months.

Nothing goes out of season quicker than a convertible, so Drive has assembled a trio of newcomers for anyone who must have the latest and greatest.

The trio of drop-tops we've lined up here are performance-based examples at three price points.

Convertibles comparison test

We pit the BMW Z4 against the Porsche Boxster S and the Mercedes-Benz SL500 in a springtime showdown.

The BMW Z4 sDrive20i kicks off the fun at $76,900, while the new Porsche Boxster S occupies the middle ground at $133,300 and the Mercedes-Benz SL500 takes the high road at $304,500.

The three also make their power in different ways. Under the bonnet of the BMW is a turbocharged inline four-cylinder, while the Porsche gets a traditional six-cylinder boxer and the Mercedes a thumping twin-turbo V8.

But despite their differences, they all promise the same thing: sporty handling, head-turning looks and comfortable, wind-in-your-hair cruising.

We took the trio to the land of broken promises, Canberra, to see if they could walk the talk.

BMW Z4 sDrive20i

The Z4 is the only two-seat sports car the company offers.

It looks the part, thanks to its long bonnet, tightly tapered rear end and low stance.

Advertisement

Once you slide into the seat you feel like you are sitting right over the rear axle, looking up over the long, chiselled bonnet.

The interior is typical BMW: simple but functional design with plenty of good-quality materials used throughout.

Small-item storage isn't great, but there is a decent glovebox and large door pockets. Boot space for those weekend road trips is limited to 180 litres with the roof down, but you can squeeze in 360 litres if you leave the lid closed.

Standard equipment in the base model includes cruise control, front and rear parking sensors, Bluetooth phone connectivity and dual-zone airconditioning. But you miss out on keyless entry and satellite navigation.

The folding metal roof, thanks to an upgrade earlier this year, can now be operated up to 40km/h.

Unfortunately, with the roof up or down, tyre roar is noticeable in the cabin, and with the roof down there is intrusive buffeting at highway speeds.

The 2.0-litre four-cylinder turbo engine is the same unit found in the more expensive 28i model, but it's tuned to produce just 135kW of power and 270Nm of torque in the 20i, compared with 180kW/350Nm in the 28i.

Initially, the 20i feels good, with enough low-rev pulling power for a fast takeoff, but it runs out of puff as the revs and speed rise.

It's available with either a six-speed manual, if you're a purist, or an eight-speed automatic transmission (with which our test car was fitted).

Having driven both, the manual is the pick, giving better freedom to get the engine in its sweet spot. The automatic is smooth around town but lacks the rapid-fire shifts you crave in a proper sports car.

The ride is good on the 17-inch alloy wheels but, pushing the Z4 through the bends, it quickly becomes apparent that it lacks the razor-sharp handling of a thoroughbred sports car. The softish suspension means there is more body lean than you'd expect.

The steering is direct but lacks feedback, not helped by the sense you are sitting so far back in the car.

In other words, the 20i is better suited to summer trips in flat countryside than challenging mountain climbs.

Porsche Boxster S

There is a new body, new interior and revised engine. We're testing the Boxster S, which adds $26,300 more than the cost of the entry-level model as well as 37kW and 80Nm.

Standard equipment includes leather trim, 10-speaker stereo, satnav, dual-zone airconditioning and Bluetooth. The interior is a big improvement on the previous model - no mean feat.

The new layout (shared with the new Cayenne, Panamera and 911) raises the centre console and gives it a more angular look. The materials and finishes used also lift the ambience.

One aspect in which the interior designers haven't improved significantly over the old model is the small-item storage, which is still sub-par.

Luggage space is also tight and spread across the front and rear, with a 150-litre space under the bonnet and another 130 litres of room in the rear.

The fabric roof is now fully electric and can open or close in nine seconds while the car travels at speeds up to 50km/h.

With the roof stowed, buffeting is minimised by a wind deflector, which makes the cabin quiet enough for conversations, even at highway speeds.

Roof up or down, the Boxster is an engaging car to drive, thanks to that flexible six-cylinder engine.

It pulls strongly from low down in the rev range and keeps building speed and aural pleasure as the revs head towards the 7500rpm red line.

The optional seven-speed dual-clutch automatic gearbox fitted to our test car is expensive, at $5300, but it provides lightning-fast shifts at speed.

From standstill, it can be a bit clunky when taking off, but for the most part it works well.

Porsche's stop-start system is one of the better examples on the market.

Ride comfort was slightly compromised by the optional 20-inch wheels (19-inch are standard) on less-than-perfect roads, but the Pirelli P Zero tyres provided plenty of grip, even when pushed hard in the corners.

The Boxster sits flat and steady in the bends, never feeling unsteady or leaving you unnerved at legal speeds.

Mercedes-Benz SL500

The SL is, in most respects, the defining Mercedes-Benz - big, powerful, luxurious and expensive.

About the only thing it isn't is subtle.

From the huge three-pointed star badge, across the vast expanse of bonnet that houses a twin-turbo V8 to the leather-lined cabin and generous-size boot, everything about the SL500 screams Mercedes-Benz.

This new model is the sixth-generation SL - a lineage that began with the iconic 300SL of 1954 - and the first all-new model since 2002.

The standard equipment list is bountiful, with highlights including hands-free access to the boot by waving your foot under a sensor mounted on the bumper, the Airscarf neck heater systems, heated and cooled seats, a 600W 14-speaker stereo with built-in TV tuner and adaptive cruise control.

But for all these goodies, the SL500's interior is actually a bit of a let-down.

It looks a little too similar to the smaller, cheaper SLK, so it lacks the real wow-factor you expect of a car costing so much.

That said, the design is classy and the materials are top-notch, so it feels premium. One area in which Mercedes has excelled is cabin storage, with plenty of space for small and large items.

Boot space, too, is generous for a convertible, with 364 litres with the roof down, which expands to 504 litres when the roof is closed.

The cabin itself is capacious, giving you a sense of space even with the roof closed, unlike most two-seater convertibles.

Even compared with the metal folding roof of the Z4, the SL's insulation is on another level.

It feels as close to a fixed-roof car as any convertible we've driven. If you want some sun, the rear wind deflector and windows cut the buffeting so much it has no impact on the cabin ambience up to 110km/h.

The twin-turbo V8 emits a deep growl and builds speed at a rate that belies the SL's size; the word effortless springs to mind.

The seven-speed auto does a slick job finding the right gear for the occasion and isn't afraid to drop down one or two cogs if you want a burst of acceleration.

The ride on the 19-inch alloys remains comfortable and composed on most surfaces, soaking up even large bumps with ease.

What the SL500 lacks is the agile handling of smaller convertibles. Despite accurate steering and the well-sorted suspension, the sheer size of the SL can't be escaped.

But while it can not truly be called a sports car, it is the grandest of grand tourers.